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Oncogenes and tumor suppressor genes

The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.

Inside the DNA of every cell in your body, there are genes—around 30,000 of them. They’re located on all 23 pairs of your chromosomes. You get one set of chromosomes from each parent, and together they determine all your physical characteristics.

  • Your genes not only dictate what eye color you have or how you smile, they also have a role in making different proteins in your body.
  • When working correctly, these proteins do a variety of things for your body, such as make sure your cells grow and divide as they should.

The role of genes in the development of cancer

However, a gene may change, or mutate itself. This isn’t necessarily a bad thing, because gene mutations may either lead to nothing or be beneficial. These beneficial mutations may even prevent you from getting certain disorders. For example, some people have a genetic mutation that prevents diabetes from developing.

Even when a gene mutation might cause problems, the body has a remarkable ability to correct these mutations before that problem happens.

But unfortunately, some mutations may lead to a person developing cancer in their lifetime. In fact, this is the way that all cancers start in the body—a result of multiple mutations that occur throughout someone’s life. Cancer doesn’t usually happen from a single mutation alone.

These changes in the gene, or mutations, are what cause a normal protein to become abnormal. Sometimes a mutation may prevent a protein from being created in the first place. When that protein isn’t working like it’s supposed to, it may result in additional DNA damage not being repaired and cause cells to start growing and dividing quickly and out of control. This is when cancer cells form in certain areas of the body.

There are two classes of genes that are tied to cancer: oncogenes and tumor suppressor genes.

So what are they, and how do they cause cancer?

Oncogenes and how they relate to cancer

It’s helpful to understand first that an oncogene is actually the name of a mutated proto-oncogene. Proto-oncogenes are normal genes in your body that help control cells dividing, growing, and even the rate at which they die off. This balance is what keeps your body healthy and working as it should.

But if there are too many copies of this gene, or it mutates, it may become hyperactivated, which means cell growth and division get out of control. Cancer cells start to form from what used to be normal cells. Once a mutation occurs, the proto-oncogene is referred to as an oncogene.

Usually, these mutations aren’t inherited, which means they aren’t passed from a parent to a child. They, like most cancers, are acquired, meaning they happen because of damage to genes. These mutations are only present in certain cells, not every cell in the body, as is the case with inherited mutations.

  • An example of an oncogene is the HER2 gene that makes HER2 protein. This protein helps control healthy breast cell division and growth. Extra copies of this gene may lead to an excess of HER2 protein, which causes cells to grow more quickly. The HER2 oncogene is found in some breast and ovarian cancer cells.
  • The RAS oncogene, another common oncogene, causes about 30 percent of cancers, including in the lungs, colon and pancreas.

Tumor suppressor genes and how they relate to cancer

Oncogenes (former proto-oncogenes) are activated and cause cells to grow and divide too quickly because of a mutation. Tumor suppressor genes, on the other hand, work slightly differently.

Tumor suppressor genes are normal genes located inside cells. Their job is to regulate cell growth and division and repair acquired DNA damage. They keep cells from growing too fast, but when mutations occur, the gene becomes inactivated or shut itself off. This causes cells to start growing out of control because the gene no longer has the ability to limit its growth and how quickly the cell divides. The result is the same as that which occurs with oncogenes—cell growth that happens too quickly and out of control, leading to the development of cancer cells.

Most of the time, like oncogenes, these mutations aren’t inherited, but acquired, meaning they happen after you’ve been born.

  • A TP53 gene mutation is the most common example of a tumor suppressor gene. In fact, more than half of the people with cancer have a mutation in this gene.
  • Other examples of tumor suppressor genes are the BRCA1 and BRCA2 genes. Everyone has these genes, and for most people, they work normally by producing proteins to keep DNA healthy. But when mutations occur, either when they’re acquired or inherited, cancer risks increase.

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